## Description
Add tests for the `backup list exchange` subcommand. Tests mostly center around indirectly testing how selectors are created and used in this subcommand by checking the output of running the `Reduce` call on a known set of `details.DetailsEntry`s. Also check various error cases
Tests for invalid formats of flag values are disabled as that code does not currently exist. These tests can be enabled when #943 is resolved
## Type of change
<!--- Please check the type of change your PR introduces: --->
- [ ] 🌻 Feature
- [ ] 🐛 Bugfix
- [ ] 🗺️ Documentation
- [x] 🤖 Test
- [ ] 💻 CI/Deployment
- [ ] 🐹 Trivial/Minor
## Issue(s)
* #913
## Test Plan
<!-- How will this be tested prior to merging.-->
- [ ] 💪 Manual
- [x] ⚡ Unit test
- [ ] 💚 E2E
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